Technical Field
The present invention relates to sanitary ware having a photocatalyst layer, which has excellent durability. More specifically, the present invention relates to sanitary ware having a photocatalyst layer, which has durability even against repeated washing under different pH conditions such as acid and alkali.
Background Art
A functional member, which has a photocatalyst layer provided on a glaze layer surface of a substrate having a glaze layer and which applies decomposition activity or hydrophilic activity of the photocatalyst, is being used in various applications. For example, a sanitary ware having a photocatalytic surface layer formed on its surface is known. Such a sanitary ware can suppress sticking of filth thereto by virtue of hydrophilicity exhibited by irradiation of light, preferably ultraviolet light, on the photocatalyst layer and, at the same time, can suppress proliferation of bacteria by virtue of decomposition action by the photocatalyst. This leads to reduction of a load of cleaning the sanitary ware.
As such a photocatalyst layer provided on the glaze layer surface, a layer comprising titanium oxide and a zirconia compound has been proposed as having good film strength, water resistance, or abrasion resistance while maintaining good photocatalytic activity (JP 2012-206907A and JP 2014-69098A).
Although a load of cleaning is reduced by the presence of the photocatalyst layer, the sanitary ware is periodically cleaned and, at which time, it is common to use a detergent having an acidic or alkaline pH. Furthermore, the sanitary ware is wiped with a brush and the like in order to remove stains, and thus physical stress is applied to the sanitary ware. The photocatalyst layer is required to have performance to endure such a load during cleaning for a long period of time, and especially performance not to lose activity of the photocatalyst and not to peel off.
On the other hand, in order to form a strong photocatalyst film, firing at a thigh temperature of 500 to 1000° C. is usually necessary. However, it is known that under such a high temperature, alkali ions in the glaze of the sanitary ware disperse and thereby deteriorate the photocatalytic activity. As a measure against this, it is known to provide an intermediate layer, which contains silica and the like as a main component and suppresses dispersion of the alkali ions, between the substrate and the photocatalyst layer (for example, JP H10-235201A, JP H11-228865A, JP 2001-152051A, and JP 2003-277056A).
These intermediate layers are, however, mainly aimed at preventing dispersion of alkalis, and according to experiments conducted by the present inventors, durability of the photocatalyst layer containing titanium oxide and a zirconia compound was inferior compared to the present invention.